I'm wondering, based on experience (and raw population data) which are the 5 "best" localizations for an application (iPhone app in this case). Note by localization I don't only mean language, but other customs such as date and currency formats, etc.
My guess list would be as follows
How does your list compare and why?
It all depends on your customers. Whom do you see as potential users of your application.
If you mean those most ready to pay, it's probably English, Japanese and German.
It should go without saying that you can't even begin to decide unless you decide where you're going to distribute your app and what it will do. Once you determine that, it should be easy to decide.
A good place to start might be to see if you can get some statistics on how the iPhone is selling in various countries. Japan is a wealthy nation, with a very tech savvy population, but if the iPhone isn't selling there it's probably not a good market. (That's just an example...I have no idea whatsoever how the iPhone is selling in Japan.)
Based solely on the most widely spoken languages,
This sort of data could be useful if you haven't yet decided what countries you want to tailor your app for. This could easily backfire on you if you don't research those populations and make sure that people who speak those languages have adequate access to technology.
Simplified and traditional chinese, to cover the markets in China, Hong Kong/Macau, and Taiwan. Although the iPhone is not officially offered in China, I'm sure Apple will reach an agreement with China Mobile or China Unicom sooner or later, opening up a potentially enormous market. Persuading people to pay is a different matter, but I can see that happening if they offer a chinese language service.
KT in Korea is also going to be officially offering the iPhone soon. There's another fairly affluent market, so Korean would be worth looking at.
Russian and Brazilian Portugese are also worth considering, as Russia and Brazil are BRIC countries etc.
And has been mentioned, English is a given, and the Japanese have now warmed to the iPhone also, despite earlier predictions.
I think your list includes the ones that pay off best for the effort of translating. A bit googling shows they rank high on the list of languages with the most native speakers (see here and here) and are at the top of the languages of Internet users. Of course you would need to know iPhone usage in the countries, but it's obvious that the countries speaking those languages rank among the tech savviest countries.
French people are very well known to insist on the usage of their own language and take their culture very serious. So it's also important to have a perfect translation and maybe adapt things to their culture.
I think your list also reflects the top foreign languages teached in school. Most Scandinavians for example speak English fluently and are used to watch uninterpreted U.S. TV shows. I wouldn't translate the app for them unless there's a very good reason.
From my own experience, I have had an unexpected and absurdly large number of sales from Italy. This is for an English word puzzle game. I have no idea why.
Updated after some spreadsheet magic:
675 sales in US
236 sales in Italy
42 sales in England
36 in Australia
1 in France
From experience the biggest markets for Localizing software are:
These countries generally have the most paying customers for software and is also in no particular order.
This list is generally referred to as FIGS+J
Adding East Asian languages can be a good idea:
Also don't forget about Russian.
There is a lot more to go on also, for example you should really have some basis for localizing your product, market research for instance. Your product might require to be internationalized, i.e. tailored to a specific country. This could be as simple as making sure the flag in your application is correct, or worse even changing content.
For example a tick to mean something is complete is pretty common everywhere but Japan when a circle means Ok.
Don't know about the other 4 languages but don't forget that the English which your other respondents place in their lists is the English spoken (and written) outside the US. If you only consider the language itself, pass this off as a joke, but when it comes to localisation (US Eng: localization) of date formats and other stuff, it probably bears more serious effort.
Regards
Mark
Brazil has a lot of internet and iPhone users. You might take that under consideration. From what i see on the streets here is that most people speak marginal english, but they (we brazilians, at least most of) will prefer a translated app.